THIS invention relates to brazing, and in particular to the brazing of PCD (polycrystalline diamond)--containing components to steel.
SNYDRILL is a trade mark used by the applicant for its range of cutters which have a thin layer of PCD sintered to a tungsten carbide substrate. The SYNDRILL cutters have been widely accepted for use on bits for the petroleum industry and in other drilling operations when the rocks which are encountered are soft or are of medium hardness. Recently developed drag bits employ far larger SYNDRILL cutters than was previously the case, and the problem has arisen of brazing the cutters to their steel backings in a manner leading to sufficient shear strength to withstand the imposed shear forces during operation.
The heart of the problem resides in the fact that the PCD layer will only remain stable for any appreciable period of time at temperatures less than 750.degree. C. This makes torch brazing a less desirable method of brazing because of the high localised temperatures. Also, experiments conducted using conventional furnace brazing techniques have proved to be unsatisfactory because of the high furnace temperatures and long retention times which are required for adequate shear strengths in the brazed connection, the end result being a reduction in abrasion resistance, and possibly even cracking, of the PCD layer.